Pre & Post Pyro Placement

[SasquatchSanta]

I'm attempting to sort out the real story on exhaust gas temperature (EGT) readings and pyrometer placement. I know this subject had been bandied about on previous posts BUT I don't think anyone has ever address temperature differentials between pre and post turbo placement.

The pyro on my Deuce is installed approximately five inches downstream of the turbo discharge. I've been told that post turbo placement is bad but no one has been able to say how bad.

If I'm going to change it, now is the time, while I have a new engine sitting on the floor.

I have a hard time believing that there would be "THAT MUCH" of a temperature differential between four-inches upstream versus five-inches downstream of the turbo. I can see 20 or 30 degrees difference but in reality, where are the BTUs in a high velocity air stream going to go?

I spoke to a friend that teaches industrial diesel mechanics at a nearby junior college. His opinion was that the difference would be insignificant. He also shared in my concerns of the possibility of the turbo eating an upstream pyro that might someday let lose.

I'd like the opinion of the those in the know SS members.

KPR (Kindest Personal Regards)

 

[BFR]

I would move it. Although you could just add another

 

[mangus580]

Keep in mind.. Heat energy is what makes the turbo spin.... so essentially the heat is transformed into motion!

 

[ken]

I've have been tought that the temp that the turbine blades are being subjected to is the consern. If they are too hot they will expand enough to rub the gas inlet casing at the volute. Oil passing through the bearing housing cools the shaft witch cools the turbine. Exaust will loose temp passing through the casing/turbine. How much? We see as much as 200deg difference. But as the say on TV "your results may vary"

 

[Djfreema]

I have also read temp differences of around 200-300 degrees. The aluminum pistons are going to start melting before you are able to do turbo damage so I think pre turbo is best to get the most accurate temps inside the combustion chamber.

 

[jasonjc]

I just got a meter for my M109A3 as the fule seem's to be UP maybe to much.( 50mph at bottom of steep hill 60mph in a few 100 feet) Looking at isspro pyrometers they have both pre and post turbo models , with about a 200-300 degrees difrance.

 

[SasquatchSanta]

Thanks for the input.

It's surprising but everything makes sense.

I could have lived with a 20 or 30 degree differential but not 200 or 300.

Guess it's time to order some gaskets and drop the turbo so I can drill and tap the manifold.

Thanks again.

 

[Dieselsmoke]

There is absolutely no reason to drop the turbo to drill and tap the manifold. If you're worried about it put some grease on your bit and tap. The shavings will be so small they will just blow right through the volute.

 

[doghead]

There is absolutely no reason to drop the turbo to drill and tap the manifold. If you're worried about it put some grease on your bit and tap. The shavings will be so small they will just blow right through the volute.

Knowing the correct place to drill would be one good reason to remove the turbo. The exhaust manifold has two chambers, so you want to drill near the center of one of them. Without removing it or having an extra gasket, you won't know the wall thickness or where the center wall is.(I don't think anyone has posted this info here)

 

[OPCOM]

Grease up the bit? Ok, I am willing, but (Dieselsmoke), you are sure about this? Also to drill slowly? Also, start with a small drill first? Do you keep replentishing the grease on the end of the drill bit? How do you do it?

 

[cranetruck]

Drilling and tapping the holes will produce a fair amount of shavings, didn't keep track of how much ended up inside, but I wouldn't want to take a chance with the turbo in place. Note two holes for choice of front or rear half of the manifold.
Having two probes will make it possible to keep track of any "missfiring" injector, not possible with post turbo probe.

 

[mangus580]

IF you drill & tap with the turbo on... attempt to do it while the engine is running. This will blow the shavings out as you break through the hole.

 

[Armada]

If your engine is currently not installed in the truck, now is the time to add the holes pre-turbo. You can plug them for now and add the probes whenever, if ever. At least the holes will be there. Even if you only plan on using one thermocouple, put in 2 holes. 2 probes can help you narrow down an engine problem though, as Bjorn said.

 

[SasquatchSanta]

Bjorn Sez:

Having two probes will make it possible to keep track of any "missfiring" injector, not possible with post turbo probe.

Is it possible to use two prodes with one pyro by using s selector switch or are you suggesting installing a second pyro?

 

[cranetruck]

You can use a selector switch.

 

[Armada]

Or a dual gauge.

 

[cranetruck]

I like the dual gauge....

 

[mangus580]

Me too.... although what I really want is a boost/pyro combo of that size...

 

[jimk]

Post turbo probes are fine. Commercial Mack trucks did this for decades. There are a few minor advantages - less thermal stress on the probe and some fail-safe should it break up(unlikely). Pre turbo has the advantage of more accurate indication of what temp the turbine wheel sees. However with the deuce there is a possibility it may be wrong if the fuel system acts up as the output from three cylinders is not being included in the EGT. This was the main reason I placed my probe post-T. Most turbo authorities see a different manifold design and offer probe location suggestions accordingly.

I would not drill above an installed turbo. Any quality instrument configuration, correctly installed, and then knowing how to read the info will get you where you want to be. Below is a good link. JimK.

http://www.bankspower.com/Tech_whyegt.cfm

 

[steelsoldiers]

I installed EGT gauges on both of my Dodge Cummins trucks. I installed them pre-turbo in the rear passage of the split manifold. The first one I did with a greased bit/tap and then used a magnet to get any remaining shavings. The second one I did without the grease, just cutting oil. I simply started the engine afterwards and let it idle to blow the shavings past the turbo. Both are widely accepted methods of installation.

Pre-turbo is much more reactive to temperature changes. You will be able to see the quick jumps in temp that the turbo would smooth out and hide. In all of my turbo-diesel tinkering over the years, I haven't met a single person who had a thermocouple fail (without help from catastrophic piston failure) and take out the turbo.

Mangus, Westach makes a quality dual EGT/Boost gauge.